analyse.js

process.env.NODE_ENV = 'production';

const webpack = require('webpack');
const BundleAnalyzerPlugin = require('webpack-bundle-analyzer').BundleAnalyzerPlugin;
const webpackConfigProd = require('react-scripts/config/webpack.config')('production');

// this one is optional, just for better feedback on build
const chalk = require('chalk');
const ProgressBarPlugin = require('progress-bar-webpack-plugin');
const green = text => {
  return chalk.green.bold(text);
};

// pushing BundleAnalyzerPlugin to plugins array
webpackConfigProd.plugins.push(new BundleAnalyzerPlugin());

// optional - pushing progress-bar plugin for better feedback;
// it can and will work without progress-bar,
webpackConfigProd.plugins.push(
  new ProgressBarPlugin({
    format: `${green('analyzing...')} ${green('[:bar]')}${green('[:percent]')}${green('[:elapsed seconds]')} - :msg`,
  }),
);

webpack(webpackConfigProd, (err, stats) => {
  if (err || stats.hasErrors()) {
    console.error(err);
  }
});

// usage via npm script
// "analyse": "node scripts/analyse.js"